The present invention relates to a method of controlling an actuator in a micro electro-mechanical device. The invention is herein described in the context of an ink jet printer but it will be appreciated that the invention does have application to other micro electro-mechanical devices such as micro electro-mechanical pumps.
Micro electro-mechanical devices are becoming increasingly well known and normally are constructed by the employment of semi-conductor fabrication techniques. For a review of micro-mechanical devices consideration may be given to the article xe2x80x9cThe Broad Sweep of Integrated Micro Systemsxe2x80x9d by S. Tom Picraux and Paul J. McWhorter published December 1998 in IEEE Spectrum at pages 24 to 33.
One type of micro electro-mechanical device is the ink jet printing device from which ink is ejected by way of an ink ejection nozzle chamber. Many forms of the ink jet printing device are known. For a survey of the field, reference is made to an article by J Moore, xe2x80x9cNon-Impact Printing: Introduction and Historical Perspectivexe2x80x9d, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
A new form of ink jet printing has recently been developed by the present applicant, this being referred to as Micro Electro Mechanical Inkjet (MEMJET) technology. In one embodiment of the MEMJET technology, ink is ejected from an ink ejection nozzle chamber by a paddle or plunger which is moved toward an ejection nozzle of the chamber by an electro-mechanical actuator for ejecting drops of ink from the ejection nozzle chamber.
The present invention relates to a method of controlling an actuator of a type that is used in the MEMJET technology and other micro electro-mechanical devices.
The invention may be broadly defined as providing a method of controlling liquid movement to and from a liquid ejection device having a nozzle chamber, a liquid ejection aperture in the nozzle chamber and a movable element located within the chamber for displacing liquid through the ejection aperture. The method comprises actuating the movable element so that it moves from a quiescent first position to a liquid ejecting second position with a first average velocity and so that it returns from the second position to the first position with a second average velocity lower than the first average velocity.
The movable element preferably is displaced from the first to the second position by application of a primary energising pulse, and displacement of the movable element from the second position to the first position preferably is retarded by application of at least one secondary energising pulse having a duration that is less than that of the first energising pulse.
The invention may further be defined as providing a liquid ejection device comprising a nozzle chamber, a liquid ejection aperture in the nozzle chamber, a movable element located within the chamber for displacing liquid through the ejection aperture, an actuator for effecting displacement of the movable element from a quiescent first position to a liquid ejecting second position within the chamber. Also, means are provided for controlling actuation of the actuator in a manner to move the movable element from the first position to the second position with a first average velocity and to control return of the movable element from the second position to the first position at a second average velocity lower than the first average velocity.
The movable element in the liquid ejection device preferably comprises a paddle which, when moved from the first position to the second position, uncovers an opening through which the liquid passes for subsequent ejection from the aperture. Also the liquid ejection device preferably includes a series of baffles adjacent the opening to inhibit the back flow of liquid through the opening during movement of the paddle from the second position to the first position.